1. Field of the Invention
The invention relates to a force detection device that detects an external force acting on a structure, and to an industrial robot having a structure to which the force detection device is attached.
2. Description of the Related Art
In recent years, industrial robots, in place of safety fences, that properly ensure the safety of humans by taking certain measures have become capable of working in cooperation with humans. This has led to increased demand for such robots, dubbed “collaborative robots”.
When a collaborative robot is used, a human and the robot share the same workspace, and it is therefore necessary to prevent the human from being injured coming into contact with the robot. Accordingly, a method is employed in which a force detection device (called a “force sensor” hereinafter) is attached to the robot main body and monitors a contact force between the human and the robot. For example, when a contact force exceeding a predetermined threshold value is detected by the force sensor, the operation of the robot is stopped or the robot is caused to operate in a manner that mitigates the contact force.
A force sensor such as that mentioned above typically includes a force sensor body that deforms under an external force as a deforming member, and a strain detector fixed to the force sensor body. The force sensor body is attached to the structure, and a deformation amount in the force sensor body is detected by the strain detector. The magnitude, direction, and the like of the force acting on the structure can be ascertained on the basis of the detected value. As an example of such a force sensor, JP-A-2009-74969 proposes a six-axis force sensor having a simple structure.
In force sensors, what is known as calibration, in which correction parameters for converting an output signal from the strain detector constituting the force sensor into a force value are calculated, is typically carried out for the force sensor alone. Thus, when the force sensor is actually attached to the structure, if the force sensor itself deforms due to deformation or surface unevenness in the area of the structure to which the force sensor is attached (called an “attachment” hereinafter), variations will arise in the above-described correction parameters. This results in a problem that error in the force value detected by the force sensor will increase.
Particularly, in collaborative robots, when the contact force detected by the force sensor exceeds the predetermined threshold value, the operation of the robot is stopped or the robot is caused to operate in a manner that mitigates the contact force. Thus, if there is an increased amount of error in the detected value from the force sensor as described above, it is necessary to set the aforementioned threshold value higher, or in other words, to set the sensitivity to contact lower, in order to avoid erroneous detection of contact. When a human and a robot come into contact, there is a limit to the contact force that the human can take, and if the sensitivity with respect to contact is low, there will be increased limitations on how the collaborative robot can be used.
Thus, in the related art, the force sensor is attached to the attachment after first eliminating deformation, surface unevenness, and the like in the attachment in order to increase the detection precision of the aforementioned force sensor. Furthermore, the force sensor is attached to the attachment over a separate highly-rigid component in order to prevent the force sensor itself from deforming due to deformation, surface unevenness, and the like in the attachment when attaching the force sensor.
However, using a method that eliminates deformation in the attachment in advance, such as polishing the entire surface of the attachment in advance, increases the manufacturing cost of the attachment.
On the other hand, with the attachment method using a separate highly-rigid component, the separate highly-rigid component is a comparatively large and heavy component, and is thus limited to an installation environment capable of withstanding heavy objects. Additionally, the separate highly-rigid component interferes with the operating region of the robot, making it necessary to limit the operating region of the robot. There is thus a problem in that this method can only be used in limited situations. In particular, there are cases where the robot is installed and used in locations aside from a floor, such as a wall or a ceiling. If the robot is heavy, the wall or ceiling where the robot is installed also needs to be reinforced, which increases the cost of preparing the installation environment. A collaborative robot can be used without a safety fence, providing an advantage in that robots can be added to or removed from production lines more easily than robots in the related art. If the robot is heavy, however, the robot cannot be moved easily, detracting from the advantage the collaborative robot provides. A separate highly-rigid component may be connected to a force sensor and provided to a user, but this increases the size and weight, which reduces the usability from the standpoint of size and makes transport difficult.
Note that, JP-A-2009-74969 has no mention whatsoever of a force sensor structure capable of ensuring that a force sensor body does not deform due to deformation, surface unevenness, and the like in an attachment when attaching the force sensor.
Having been achieved in light of the above-described problems, an object of the invention is to provide a force detection device having a structure that improves the accuracy at which a force is detected, and a robot including the force detection device.